He uses more then one lay-out of wich you can choose from, for example heal lay-out puts the castbar on top of the actionbars.
(just pointing this out he probably uses some others in-game /commands) or download his in-game config wich also contains dozen of options

I prefer Elvui to default Tuk as the config options are MIIIILES better. Getting the casterbar like that in Elv is easy, there's an option in the config under "castbar" labelled "use larger castbar" - just tick that and it makes it look like that

I prefer Elvui to default Tuk as the config options are MIIIILES better. Getting the casterbar like that in Elv is easy, there's an option in the config under "castbar" labelled "use larger castbar" - just tick that and it makes it look like that